Rectifier transformer having means for obtaining forming voltages without additionalwindings



y 1958 D. R. VERNER ET AL 2,843,816

RECTIFIER TRANSFORMER HAVING MEANS FOR OBTAINING FORMING VOLTAGESWITHOUT ADDITIONAL WINDINGS Filed Aug. 2, 1955 2 Sheets-Sheet 1 y 5,1958 D. R. VERNER ETAL 2,843,816

RECTIFIER TRANSFORMER HAVING MEANS FOR OBTAINING FORMING VOLTAGESWITHOUT ADDITIONAL WINDINGS Filed Aug; 2, 1955 2 Sheets-Sheet 2 HOD 0H0IF {i 12 I )6 3 /6 I I L3 /6 1? I 4 I w a? i /a.' I15 7:

United States Patent RECTIFIER TRANSFORMER HAVING, MEANS EOR OBTAININGFORMING VOLTAGES WITHOUT ADDITIONAL WINDINGS Dalton R. Verner andLawrence M. Stoakes, Pittsburgh,

Pa., assignors to Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

Application August z, 1955, Serial No. 525,848

4 Claims. (Cl. 321-8) This invention relates in general to an electriccurrent conversion system having an alternating current circuit, arectifying transformer, a plurality of electric valves, and a directcurrent circuit. The invention relates in particular to an improvedarrangement of the windings on the rectifier transformer and theconnection of the windings to the valves so that the transformer isoperable to selectively supply operating voltages to the valves orforming voltages to the valves to simultaneously bake out all thevalves.

In electrical current conversion systems which employ ionic valves suchas mercury arc rectifiers to translate energy from a supply circuit toaload circuit, means must be provided to supply reduced voltages to theanodes of each valve in addition to supplying normal operating voltages.This is because when the valves are to be initially energized or havebeen deenergized for a period of time, the reduced voltage is employedto drive off occluded gases in the valve prior to energizing theconversion system with operating voltages. This reduced voltage is oftenreferred to as a forming voltage and the period during which it isapplied to the valves is referred to as the bakeout period.

Various transformer winding arrangements have been suggested in theprior art which are operable to selectively supply either normaloperating voltage or forming voltage to the anodes of the valve.However, these prior art-transformer arrangements are expensive to buildbecause of their construction and usually have one or more disadvantagesin operation. In some instances the windings of the transformers aretapped to provide the two different volt'ages. Such a winding is moredifficult and more expensive to build than a winding without taps.Several other suggested arrangements involve altering the taps .on oneor the other of the windings of the transformer to provide the formingvoltage. In other instances extra windings are provided on thetransformer which operate solely during the baking out period.

It has been found that the disadvantages of the systems embodying theteachings of the prior art may be avoided by the present invention. Thepresent invention provides a winding arrangement for the transformer inwhich groups of windings may be selectively connected in one manner tosupply normal operating voltage to the anodes of the valves, orconnected in another manner to supply forming voltages simultaneously toall the anodes to simultaneously bake out all the valves.

It is therefore an object of the present invention to provide in anelectrical conversion system employing ionic valves, an improvedtransformer winding arrangement for selectively supplying operatingvoltages to the valves or .for supplying forming voltages to the valvesto simultaneously bake them out.

Another object of the present invention is to provide in a currentconversion system including an alternating cur rent circuit and aplurality of ionic valves, an improved transformer winding arrangementfor connecting the anodes of the valves to the supply circuit to supplyeither operating or forming voltages to the valves without the icedirect current of the conversion system affecting the per formance ofthe rectifier transformer.

A further object of the present invention is to provide a rectifyingtransformer having windings which do not require taps in order toselectively supply both operating and forming voltages to ionic valvesin a current conversion system.

A still further object of the present invention is to provide in aCurrent conversion system a rectifying transformer having windings whichare used to supply both operating voltages and forming voltages to theionic valves. v

Objects and advantages other than those mentioned above will be apparentfrom the following description when read in connection with drawings inwhich:

Fig. l is a diagrammatic view of the current conversion system embodyingthe improved transformer connected to supply forming voltages to thevalves;

Fig. 2 is a diagrammatic view similar to that shown in Fig. 1 with thetransformer arrangement connected to supply operating voltages to thevalves; and

Fig. 3 is a schematic illustration of the transformer shown in Fig. 1.

Referring to the drawings, the system illustrated in Fig. 1 comprisesgenerally an alternating current supply circuit 11, a direct currentload circuit 12, a plurality of electric valves 13, and the improvedrectifying transformer 14 for connecting the anodes 16 of the valves 13to the A. C. supply circuit 11.

Each ionic valve 13 comprises an anode 16, a cathode of theself-reconstructing type such as a mercury pool cathode 17, and a gridmember 18. Inasmuch as the grid voltage supply circuit forms no part ofthe present invention and since any of the various grid voltage supplycircuits suggested in the prior art may be used, a discussion and ashowing of that portion of the rectifying sys tem has been omitted.

The transformer winding arrangement as shown comprises a three phasecore, three primary windings and twelve separate but related secondarywindings. The primary and secondary windings of the transformer arerepresented by lines whose lengths and directions correspond to themagnitude and phases of the voltages in them according to the usualconvention. The three primary windirigs 21 of the transformer as shownare conne ted in delta to the three phase alternating supply circuit 11but if desired the primary windings may be connected in star to supplycircuit 11. The secondary windings are connected in a double stararrangement to the valves 13. The neutrals of the double stararrangement are connected to opposite ends of an interphase transformerhaving a midtap connected to one conductor of the load circuit 12. Thecathodes 17 of all the valves are connected to a cominon bus which inturn is connected to the other conductor of the load circuit.

The three phases of the transformer winding arrangement are similar soonly one is described in detail. Each phase'comprises a primary winding21, a first group of windings 22 and a second group of windings 23 whichare disposed electrically degrees from the first group. Each group ofwindings comprises a main winding designated by reference character aand an auxiliary winding designated by reference character b, the mainwindings a of each group having a like number of turns and the auxiliarywindings b of each group a like number of turns. However, the number ofturns for the auxiliary windings b are less than those of the mainwindings a. The first groups of secondary windings are disposed todefine one of the star arrangements by connecting the first ends 26 ofthe main windings 22a to the neutral point of that star. The secondgroups of secondary windings are similarly disposed to define the otherstar arrangement by connecting the first ends 27 of the main windings23a to the neutral point of that star.

The transformer arrangement also includes means for connecting the foursecondary windings of each phase of the transformer so that thesecondary windings may selectively supply both forming and operatingvoltages to the anodes of the valves associated with their respectivephases.

The means for connecting the four secondary windings of each of thethree phases to their associate valves is similar and a detaileddescription with respect to one phase is considered suflicient. One end29 of each auxiliary winding is connected to a diflierent valve 13associated with that phase. As shown, the means for interconnecting theends of the main and auxiliary windings between the two associatedvalves and the respective neutrals of the star arrangements comprises aswitch 36 having four contacts and a pair of bridging members adapted tobridge separate pairs of contacts. The contacts of the switch arearranged so that the main winding 22a and the auxiliary winding 22b maybe connected together in substractive series relationship and also sothat the main and auxiliary winding 23a and 23b may be connectedtogether in subtractive series relationship to cause separate formingvoltages displaced 180 degrees from each other to be suppliedsimultaneously to the two valves 13 associated with that phase of thesystem.

As shown, this is accomplished by connecting the second ends 37 of thetwo windings 22a and 22b to contacts 38 of the switch 36 which may beconnected together by a bridging member 39. Likewise, the second ends 42of the two windings 23a and 23b are connected to contacts 41 on theswitch 36 which may be connected together by a second bridging member43.

The secondary windings associated with the remaining two phases of thesystem are similarly connected to like switches so that with theswitches 36 in the position as shown in Fig. l, the system is incondition when energized to simultaneously supply forming voltages toall the anodes to bake out all the valves at the same time.

After the required bakeout period the switches 36 may be moved toanother position as shown in Fig. 2 to supply normal operating voltagesto the valves.

For example, as shown in Fig. 2 the bridging members 39 and 43 of eachswitch may be positioned to bridge a pair of contacts different fromthose used for the forming voltages so that for each phase the mainwinding a of each group is connected in additive series circuit with theauxiliary winding b of a different group. As shown in Fig. 2 thebridging member 39 is in position to bridge contacts 38 and 41 whichconnect the second end 37 of the main winding 22a of the first group tothe second end 42 of the auxiliary winding 23b of the second groupcausing these windings to be in additive series circuit to supply normaloperating voltage to the anode of one of the valves 13 associated withthat phase. Similarly, the other bridging member 43 is positioned tobridge contacts 38 and 41 which connect the second end 42 of the mainwinding 23a of the second group to the second end 37 of the auxiliarywinding 22b of the first group causing these windings to be in additiveseries relationship to supply a normal operating voltage to the anode ofthe other valve associated with that phase.

It will be seen that with the improved transformer, forming voltages andoperating voltages are selectively supplied to the valves by merelymoving a switch from one position to another. The need for tappedwindings is eliminated resulting in considerable saving of time andlabor in manufacturing the transformer. Also, the bakeout period isconsiderably reduced in that forming voltages are suppliedsimultaneously to all the valves.

While the preferred embodiment of the present invention is shown havingfour position dial type switches associated with each phase, it will bereadily seen by those skilled in the art that other type switches may beemployed to etfect the results obtained by the dial switches withoutchanging the operation of the system.

It will also be seen by referring to Fig. 3 that the windings arearranged on the transformer core so that the direct current of theconversion system does not affect the operation of the rectifiertransformer. As shown in Fig. 3, the primary winding 21 and the foursecondary windings 22a, 22b, 23a and 23b associated with the primarywinding 21 are disposed on a single winding leg 50 of core 57 and thewindings of the other two phases are similarly disposed on the remainingtwo legs 52 and 53 of the core. With the windings so arranged on thecore the current in the load circuit does not affect the operation ofthe transformer.

While only one embodiment of the present invention has been illustratedand described it will be apparent to those skilled in the art thatmodifications may be made therein without departing from the inventionor from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. An electric current conversion system comprising an alternatingcurrent circuit, a direct current circuit, a plurality of ionic valves,three phase transformer means comprising three primary windingsconnected to said alternating current circuit and secondary windingsconnected in double star arrangement to said valves to selectivelysupply operating and forming voltages to said valves, each phase of saidtransformer means comprising one of said primary windings, four of saidsecondary windings inductively related to said one primary winding, andswitch means, said four secondary windings comprising first and secondgroups of windings displaced electrically degrees with respect to eachother, each said group of windings comprising a main winding and anauxiliary winding having fewer number of turns than said main winding, afirst end of each of said main windings connected to the neutral of adifferent star of said double star arrangement, a first end of each ofsaid auxiliary windings connected to separate ones of said plurality ofvalves, and means connecting the second ends of said windings in saidfirst and second groups to said switch means to cause said switch in oneposition to connect said main and auxiliary windings of different groupsin additive series relationship to supply operating voltages to saidseparate valves, and to cause said switch in a second position toconnect the main and auxiliary windings of the same group in subtractiveseries relationship to supply forming voltages simultaneously to saidseparate valves.

2. An electric current conversion system comprising an alternatingcurrent supply circuit, a direct current load circuit, a plurality ofionic valves, three phase transformer means connected in delta to doublestar arrangement between said supply circuit and said valves toselectively supply operating and forming voltages to said valves, eachphase of said transformer means comprising a primary winding, foursecondary windings inductively related to said primary winding, andswitch means comprising four contacts and a pair of bridging membersoperable to bridge different pairs of said contacts, said four secondarywindings comprising first and second groups of windings displacedelectrically 180 degrees with respect to each other, each said group ofwindings comprising a main winding and an auxiliary winding having fewernumber of turns than said main winding, a first end of each of said mainwindings connected to the neutral of a different star of said delta todouble star arrangement, a first end of each of said auxiliary windingsconnected to separate ones of said plurality of valves, means connectingthe second ends of said windings in said first and second groups todifferent ones of said contacts, said bridging members being operable tocause said switch in one position to connect said main and auxiliarywindings of different groups in additive series relationship to supplyoperating voltages to said separate valves, and to cause said switch ina second position to connect the main and auxiliary windings of the samegroup in subtractive series relationship to supply forming voltagessimultaneously to said separate valves.

3. An electric current conversion system comprising an alternatingcurrent supply circuit, a direct current load circuit, a plurality ofmercury arc rectifiers, three phase transformer means connected to deltato double star arrangement between said supply circuit and saidrectifiers to selectively supply operating and forming voltages to saidrectifiers, each phase of said transformer means comprising a primarywinding, four secondary windings inductively related to said primaryWinding, and switch means comprising four contacts and a pair ofbridging members arranged to bridge different pairs of said contacts,said four secondary windings comprising first and second groups ofwindings displaced electrically 180 degrees with respect to each other,each said group of windings comprising a main winding and an auxiliarywinding having fewer number of turns than said main winding, 21 firstend of each of said main windings connected to the neutral of adifierent star of said delta to double star arrangement, a first end ofeach of said auxiliary windings connected to separate ones of saidplurality of rectifiers, means connecting the second ends of saidwindings in said first and second groups to different ones of saidcontacts, said bridging members being operable to cause said switch inone position to connect said main and auxiliary windings of difierentgroups in additive series relationship to supply operating voltages tosaid separate rectifiers, and to cause said switch in a second positionto connect the main and auxiliary windings of the same group insubtractive series relationship to supply forming voltagessimultaneously to said separate rectifiers.

4. In combination a three phase rectifying transformer having itswindings arranged to be connected in a delta to double star between analternating current circuit and a plurality of mercury arc rectifiers,each phase of said transformer comprising a primary winding and foursecondary windings inductively related to said primary winding, saidfour secondary windings defining first and second groups of windingsdisplaced electrically degrees with respect to each other, each saidgroup of windings comprising a main winding and an auxiliary windinghaving fewer number of turns than said main winding, a first end of eachsaid main winding connected to a neutral of a different star of saiddelta to double star arrangement, a first end of each said auxiliarywinding connected to separate ones of said rectifiers, and switch meanscomprising a first pair of contacts connected to the second ends of saidmain windings, a second pair of contacts connected to the second ends ofsaid auxiliary windings, and a pair of bridging members, said bridgingmembers in a first position of said switch arranged with respect to saidpairs of contacts to connect said main winding of said first group tosaid auxiliary winding of said second group in additive seriesrelationship, and said main winding of said second group to saidauxiliary winding of said first group in additive series relationship,and in a second position of said switch arranged with respect to saidpair of contacts to connect said windings of said first group insubtractive series relationship and said wind ings of said second groupin subtractive series relationship.

References Cited in the file of this patent UNITED STATES PATENTS1,804,614 Hill May 12, 1931 1,912,151 Leuthold May 30, 1933 2,206,701Klemperer July 2, 1940

